1. Field of the Invention
The present invention relates to a cutting tool specifically suitable for use in machining of valve bores of a cylinder head of an internal combustion engine.
2. Description of the Related Art
Brims of valve bores formed in an engine cylinder head are frequently impacted by valves. It is, therefore, a common practice to fit a member of a hard material such as a sintered alloy to improve durability of the brim portions of the valve bores. In order to machine such a valve bore, therefore, a cutting tool is used which has both a boring cutting portion such as a gun reamer for finishing the bore itself and a cutting insert for machining the open brim portion of the bore. Usually, the brim of the valve bore is conically-shaped in conformity with the shape of the valve head. In order to machine such a conical brim, the above-mentioned cutting insert is preferably mounted in such a manner as to be slidable in a direction which obliquely intersects the axis of rotation of the cutting tool.
FIGS. 8 and 9 show an example of a conventional cutting tool which is used in machining valve bores of the kind described.
The cutting tool has a generally cylindrical tool body 1 and is mounted through an adapter 2 on, for example, a spindle of a lathe which is not shown, so as to be rotated about the axis O of the spindle. A bush 3 is mounted on the end of the tool body 1 so as to extend along the axis O. The above-mentioned boring tool, such as a gun reamer (not shown), is inserted to the bush 3 at its shank portion, so that the boring tool is fed while being rotated together with the tool body 1, thereby boring and finishing a bore. The feed of the boring tool is effected by means of a shaft which is coaxially received in a slide shaft which will be described later.
Three cutting inserts 5A, 5B, 5C are provided on the outer periphery of the end of the tool body 1. The open brim of the bore is machined by these cutting inserts. FIG. 8 shows only one, 5A, of the cutting inserts, while other cutting inserts, 5B and 5C, are omitted from the drawings.
Among these cutting inserts 5A, 5B and 5C, two cutting inserts 5B and 5C are directly fixed to the tool body 1, while the remaining cutting insert 5A is mounted slidably as explained before. More specifically, a T-shaped groove 6 is formed in the tool body 1 extending in a direction of a generating line of the cone of the tool body 1, i.e., in a direction which obliquely intersects the axis O, as shown in FIG. 8. The T-shaped groove 6 is also shown in FIG. 9. The T-shaped groove slidably receives a slider 7. The above-mentioned cutting insert 5A is detachably fixed to this slider 7.
On the other hand, bores 1a and 2a are formed in the adapter 2 so as to extend along the axis "O". These bores 1a and 2a receive a slide shaft 8 and a coupling member 9, respectively. The coupling member 9 is fitted in these bores through the intermediary of a key 9a, so that the tool body 1 and the coupling member 9 as a unit are rotatable about the axis O. At the same time, the coupling member 9 is slidable back and forth in the bore 1a as the slide shaft 8 is moved back and forth. The T-shaped groove 6 in the tool body 1 communicates with the interior of the bore 1a via a hole 6a which is formed so as to open in the bottom of the T-shaped groove 6. A connector pin 10 which is connected to the slider 7 projects into the bore 1a through the hole 6a. The connector pin 10 has an end received in a slant hole 9b formed in the coupling member 9, so as to interconnect the slider 7 and the coupling member 9, whereby the slider 7 is made to slide along the T-shaped groove 6 in the tool body 1 in accordance with the back and forth movement of the coupling member 9 caused by the movement of the slide shaft 8, thereby causing the cutting insert 5A to slide in a direction which obliquely intersects the axis O.
The machining of a valve bore with this type of cutting tool is conducted in the following manner. A boring tool such as a gun reamer is mounted in the bush 3 and is retracted towards the base end of the tool body 1 by means of the shaft 4. Then, the tool body 1 is fed in the direction of the axis O while being rotated, whereby the open brim of the bore is chamfered by the cutting inserts 5B and 5C. Then, the tool body 1 is slightly retracted and, while the tool body 1 is rotated, the slide shaft 8 and the coupling member 9 are advanced to cause a sliding motion of the cutting insert 5A through the connector pin 10 and the slider 7, whereby a tapered surface is formed on the open brim of the bore. Then, the shaft 4 is operated to forwardly feed the boring tool while the tool body 1 is being rotated, thereby finishing the surface of the valve bore.